This is a minor bug, already fixed in 8.0.
mysqltest: At line 38: query 'SHOW BINLOG EVENTS FROM 1 LIMIT 1' succeeded - should have failed with errno 1220...
SHOW BINLOG EVENTS FROM <bad offset> is not diagnosed inside Format_description_log_events
5.7 - SHOW BINLOG EVENTS FROM is not diagnosed for high invalid offsets
8.0 - SHOW BINLOG EVENTS FROM is not diagnosed for high invalid offsets