Entering Germany with COVID-19 border regulations

I'll give a purely practical answer without digging too much into the academics.

Your first concern needs to be getting on the flight. For this, airport staff will use the TIMATIC database, which states:

Passengers arriving from a non-Schengen Member State are not allowed to enter Germany.

This does not apply to passengers with long-term right of residence (residence permit or longer-term visa) in an EEA Member States, Switzerland or the United Kingdom, returning home

A Blue card is a residence permit - Aufenthaltstitel - the word being printed on the card.

Now, the information in TIMATIC comes from section 22 of the Bundespolizeipräsidium, and as such is bound to be correct. Therefore, you can fly to and re-enter Germany.

So my question is, is the Blue Card considered a "long-term resident"?

Someone with a blue card is not a "long-term resident[] under the Long-term Residence Directive." However, such a person is a "person[] deriving [a] right to reside from...national law." Therefore, the bearer of a valid German blue card should be permitted to return to a home in Germany.

The term "long-term resident" denotes a beneficiary of Directive 2003/109/EC of 25 November 2003 concerning the status of third-country nationals who are long-term residents, referred to in the quoted text as "the Long-term Residence Directive." To be a beneficiary of this directive, you must have lived in Germany for at least five years.

However, the text that you have received from the consulate seems like a judicial or other decision that places limits on the "temporary travel restriction," not a description of the actual terms of the restriction itself. Without more context from the message you received, it's impossible to say what the terms of the restriction actually are.

At Coronavirus and entry restrictions: 4 things travelers to Germany need to know, which is five days old as of this writing, the German foreign ministry says that it will allow foreigners holding any residence permit for another EU country to transit through Germany in order to return to the country of residence, but they do not explicitly cover non-Germans who reside in Germany:

EU-citzens and citizens of Great Britain, Iceland, Liechtenstein, Norway and Switzerland and their family members will be allowed to transit through Germany to reach their home countries. The same will apply for foreigners holding a residence permit in one of these countries.

However, any residence permit is probably included in "a national long-term visa," even though it is not strictly speaking a visa. Your blue card is a residence permit, so you are probably fine to return home.

Yes, the Blue Card is one form of a residence permit.

Long is anything that is at least 3 months.

Within Germany, returning to your place of residence is considered a valid travel reason.

Assuming you have your card with you, you should have no problems with either the Airline or Border guards.

Personen, die nicht die deutsche Staatsangehörigkeit haben, dürfen unter folgenden Bedingungen einreisen :
...
Zur Heimreise nach Deutschland zum gewöhnlichen Aufenthaltsort bzw. Wohnsitz.

Persons who are not of German nationality may enter under the following conditions:
...
To travel home to Germany to their usual place of residence or domicile.

This should be clear enough for everyone to understand.

The German term längerfristigen Aufenthalts means, as it is used in the German law terminology, long term presence (can be longer than 90 days).

Kurzfristiger Aufenthalt is the opposite, short term presence (presence of maximum 90 days - C-Visa, Schengen Visa).

The meaning of these terms should not be confused with similar terminology used in other jurasdictions where the definition may be different. In translations residence is often used, but should not be confused with residence permit or a D-Visa (which allows a long term presence).

Sources:

• BMI - Alle Meldungen - Wichtige Hinweise zu vorübergehenden Grenzkontrollen und Einreisebeschränkungen