It doesn't make any sense regardless how you look at it.
Blast was at a parallel dimension before the fight against Cosmic Garou started.
If time travelling created a parallel world as Genos suggested, said parallel world cannot include Blast, as he was in a parallel dimension (and parallel dimensions in OPM have shown to have their own flow of time, check when Saitama met God for example), so if it was the same Blast as the one in the future, then he should remember everything. Other option is that there are countless Blasts fighting the same entity, yet they do not cooperate
If time travelling just rewinded time before the beginning of Garou fight, it makes even less sense. If Blast went back to the "Another Dimension" he was before the fight begun, then he shouldn't be affected by the time rewind. And if he didn't, then it's even more weird because the time travel went to a point before he arrived, so... where did he go?