How can a travel agent issue cheap tickets just a few hours before a flight?

Update: After asking this TA whether he is a 'consolidator' he said he didn't know this word (apparently). Anyway I will accept Kate's answer for now as no one else has given a better answer.

Question:

A friend of mine told me about this travel agent (TA). The friend is buying tickets from this agent since 2 years.

The friend usually contacts the TA month or two in advance and the TA gives him a flight itinerary with HK (Holding Confirmed) category/number. These tickets are much cheaper than the ones we see online, usually 10-15% cheaper.

• The TA does actual issuing of tickets 12 hours - 2 hours or so before the travel. The TA says he issues the tickets for every client (who travel on the same day), at the same time (i.e. issues tickets of the whole group at once).

I want to understand what kind of business model this is. The TA says he is an authorized travel agent.

• The TA did not explain to me why he waits for so long and issues tickets a few hours before the flight to get the special cheap ticket price.

• TA says he does not contact airline at the last minute and the tickets are already confirmed.

• TA says he does something in his "system" to issue the tickets (without contacting airline). He did not explain further.

I don't understand why he does it this way. Do you know why some travel agents give HK number months in advance but issue tickets a few hours before the flight?