It's deja vu all over again

The reasons for my recent obsession with sets and their redraws became clear today:

PokerStars Pot-Limit Hold'em, $0.25 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: HTML)

MP3 ($14.75)
CO ($4.80)
Button ($14.65)
Hero ($25.50)
BB ($62.20)

Preflop: Hero is SB with 7s, 7d.
4 folds, MP3 calls $0.25, CO calls $0.25, 1 fold, Hero completes, BB checks.

Flop: ($1) 4s, 7c, 6h (4 players)

There's that flopped set again, and top set too. Someone said to bet your sets so:

Hero bets $0.5, BB raises to $1.5, MP3 folds, CO folds, Hero raises to $4.5, BB calls $3.

Now that's a bit odd -- he checked preflop, raised my flop bet, and then called my raise. What's he got? Two pair? Another set? Flopped straight?

Turn: ($10) 4d (2 players)

Unless it was 44, it doesn't matter any more. Now how much can I get into the pot?

Hero bets $4, BB calls $4.
River: ($18) Qh (2 players)
SB bets $10, BB calls $10.

Final Pot: $38

And indeed he had 58.