Export of custom multiple choice options to CSV files limited to 32 characters
Ahh it's a field of type number, which means it's getting set here: https://github.com/civicrm/civicrm-core/blob/77c3b7089c290880a7599cc77cdbe87fa6958c13/CRM/Export/BAO/ExportProcessor.php#L1498.
So yes if it's an option list then there's a mismatch. You could work around it by defining the field as type string instead and still use numbers as the values. But yes in general it seems like a bug - you could file a ticket at https://lab.civicrm.org/groups/dev/-/issues