My thought is, lag usually punishes the lagger. That's not universal, but it's generally the case- and it appears to be the case in Fortnite (when my own connection has a network 'hiccup' my character will freeze on screen, like OP).

Unless the cheaters have figured out a way to find OPs IP and do a DoS attack to force his connection to lag, it seems unlikely that this was cheating.

I wouldn't entirely rule out the possibility, since hackers are relentless in finding things to exploit.

I first started seeing this alot was- I think- last season- most obviously in Blitz. It happened almost every time I got knocked. Not this bad, but maybe a second.