That's specific to BT TV 4K. They require a minimum of 44Mb to order the service. They throw in Infinity 2 free for 12 months all the time. They are then Infinity 2 customers and the price will go up after 12 months or they can recontract.
These upgrades are BT taking advantage of an OpenReach offer that's only been in effect since April. Talktalk have been moving many users from 40/2 to 40/10 as part of the offer.
Bandwidth Modify Special Offer for existing GEA-FTTC lines upgrading to a higher speed tier
With this deal the customer remains on Infinity 1, just at a higher speed.