Chances are that the swap out happened earlier. Log into the host via SSH and run e.g.:

memstats -r vm-stats -s name:b:memSize:min:max:consumed:ballooned:balloonTgt:swapTgt:swapped:active:touched:zipped:zipSaved:shared:zero:sharedSaved -u mb 2> /dev/null | sed -n '/  \+name/,/ \+Total/p'

To check memory stats of your running VMs.