The mxcfb refresh ioctl is likely the cause of the wakeup, I can't see anything else having any potential effect (EDIT: And I don't see anything unexpected in a strace run, either). Unless disk I/O counts, somehow, but that only happens with TTF/OT fonts (EDIT: Not really, device ID requires disk I/O, too).
At least, I can see that waking the kernel. Not quite sure how that could ever translate to a touch event, though :?.
EDIT: You can test that theory by enabling --norefresh.
If you start decoding the input events, having a specific idea of exactly *which* kind of event that is might be helpful

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/sys/power/state-extended *should* return 1 right before a suspend, but I don't rightly remember how Nickel times all of this, so this might not actually be usable.