Shiozaki: Wait a minute, did you just summon a bunch of frog heroes for one battle?
Tsuyu: Yeah, so?
Shiozaki: That's against the rules, isn't it?
Tsuyu: Screw the rules, we have green hair.

If I had to guess, based on the image before this part where she pulls back her sleeve showing her skin covered in some sort frog slime (mucus I guess?), she most likely put it on her team mates so that they'd all smell like her, thus throwing off the big guy on the other team. There aren't actually 3 of her, but as far as his nose is concerned, there are, so he doesn't know who is who or what to expect.