Hi,
This is in any case a single flow because the flow is bidirectional.
If the reverse route lookup is performed while processing the response packets and how it is performed depends on "set flow reverse-route ...". The default setting is "set flow reverse-route clear-text prefer". This means (as explained in the CLI guide):
clear text prefer
—Perform reverse route lookup during session
creation. If a route is found, use that route. If no route is found,
traffic arriving in the reverse direction is sent back using the cached
MAC address. This is the default.
You can also find a couple of KB articles using "set flow reverse-route " and "set arpalways-on-dest" as a search criteria.