the switch records the current situation and reloads the file across reboots.
afaik it is NOT a static DHCP-assignment. but as the client will request re-use of the same ip-address it has used before, it will most likely behave as static assignment.
for real static assignment you need
SUMMARY STEPS
1. enable
2. configure terminal
3. ip dhcp pool pool-name
4. host address [mask | /prefix-length]
5. client-identifier unique-identifier
6. hardware-address hardware-address [protocol-type | hardware-number]
(7. client-name name )
8. end