(1) These tieflings are still all infernal-based, if anything 5e SCAG made tieflings far more Asmodeus-only than 4e actually did (see below).
(2) The actual 4e lore was that the human nobles who would become tieflings made pacts with the devils of the Nine Hells. We are never told that it was with Asmodeus or that tieflings were an Asmodeus-only thing. Far from it. 4e Tiefling book, p. 4:
That's pretty much it. Nowhere does it specify that tieflings were an Asmodeus-only thing, only that it was pact with the devils of the Nine Hells. This lines up with tieflings in the PHB, the SCAG, and MToF in 5e, which are still infernal-based.
Edit: Checked and the name "Asmodeus" does not even appear in the Tiefling race description, again only that the tieflings' ancestors made pacts with devils.
In fact the Asmodeus-only stuff comes more from 5e than 4e!
5e PHB (p. 42):
And since you like talking about the alternate tieflings that SCAG provided, then I'm sure you are incredibly well-versed in what that text says, so I won't quote all that here.
But sure, I get it. It's easier to blindly complain about what 4e did without knowing much about it.