Refused entry at Gare du Nord due to stolen BRP

My UK biometric residence permit (BRP) was stolen in Paris and I was not allowed to board my return flight. I was advised to try Gare du Nord as you could speak with an immigration officer there, who might let me in after explaining my situation. I had my passport, photo of my BRP, etc. Guess what, they did not let me in.

Now I am waiting for my replacement BRP visa, but I am very worried about the refused entry record. They put a cross on the stamp in my passport, and issued me with a refusal to leave to enter letter. I was in shock at the time and I only asked the immigration officer whether this would be on the immigration record, and he said "there would be a note of this encounter but this wouldn't affect you". He seemed very flippant about this so I didn't ask for more details.

Now that I've had some time to think I'm really worried about this. Does this count as 'adverse immigration history'? Do I have to declare this every time I make a visa application, when they ask about "have you ever been refused entry at the UK border"?

The notice they gave me was a simple one page thing that had a Port reference, but no HO reference. It also had a COH ID. But it didn't look anything like the refused visa letters I've seen on here (no mention of appeal or anything like that). In the main paragraph, it said they were refusing entry because I could not produce a BRP, under Paragraph 245HA of Appendix V of Immigration Rules.

I looked it up; it only says valid entry clearance required blah blah. The problem is: even the immigration officer admitted they could see on the system I had a Tier 2 visa, they just needed the physical card (which was stolen!)

All in all, my questions are basically:

1. Does this "encounter" constitute "refusal of entry"?
2. Does this mean I have to declare it from now on in all visa applications?
3. How serious is this?
4. Is there any way for me to mitigate any adverse effects, now that this has happened?