Can someone explain this?

[plethodon]

I was playing a 5 handed NL tournament at Pacific and two plays baffled me.

The first one happened when it was folded around to the blinds. The player in the SB bet $600 (blinds were 25/50 and he had $800) and the BB called him. Then on the flop, the SB just folds first thing.

Later the same two guys were in the blinds again and it was folded around to them. The SB completed and the BB went all in. The SB called him (it left him with $79). Then the SB folded once the flop hit (at Pacific the player with money left can fold/check/bet once after the all in - I'm not sure if that's the case everywhere). This gave the BB a large chip lead.

I'm pretty new to this, but is there a legitimate reason one would do this type of thing or were they cheating?