[50NL] 99 vs short stack

[vanoff]

Ultimate Bet - No Limit Hold'em Cash Game - $0.25/$0.50 Blinds - 6 Players

SB: $49.50
BB: $41.45
<font color="green">UTG</font>: $19.60
<font color="red">Hero (MP)</font>: $50.00
CO: $34.30
BTN: $24.05

Preflop: Hero is dealt (6 Players)
<font color="green">UTG raises to $1.75</font>, <font color="red">Hero raises to $6.00</font>, 4 folds, <font color="green">UTG calls $4.25</font>

Flop: ($12.75) (2 Players)
<font color="green">UTG checks</font>, <font color="red">Hero bets $13.60</font>


I'm just wondering.. is this the standard line vs a unknown short stack?
Or am I spewing because he's only calling with a K or a set? Maybe because I'm reading him as incompetent he'd call on a FD..