The feedback loop, for starters. Traditional unity gain SK would have the schemetic's R6 going straight back to the junction between C3 and C4. Instead, there is a "tap" from a very high ratio divider that then also connects to the inverting input. Let's presume that's because they want an SK filter with gain (possible but tricky)... in that case you generally use a more traditional dedicated divider from the output to the inverting input, leaving the positive feedback loop separate to handle its filtering functions.
If R6 and R5 are intended to be a negative feedback divider, that's a HECK of a lot of gain for an SK configuration (A = 330) and R5 would be tied to ground, not in the filter network. On the other hand, if R5 and R6 are part of the filter network, then why is there a connection to the inverting input? That's not part of a normal SK filter design.
Maybe this is some derivation of an SK. Hopefully someone will chime in if so.