You are vulnerable against not.
Partner dealt.
Pass over 4♠ is NOT forcing (hence the two of a non-kind)
You and your partner are fairly solid players
LHO is sometimes imaginative in the auction
RHO is hyper-aggressive in the auction
(same players as the other hand, but rotated)

Help

1♦ 1♠ 2♥ 2♠
4♥ 4♠ ?