Question

Does this mean I can’t update another table from a trigger if I’m using MySQL < 5.0.10

MySQL documentation:

Note Before MySQL 5.0.10, triggers cannot contain direct references to
tables by name. Beginning with MySQL 5.0.10, you can write triggers
such as the one named testref shown in this example…

Answer 1

This is correct. This FAQ states this fact in a less ambiguous way:

Before MySQL 5.0.10, a trigger cannot modify other tables

Please note the following limitation still exists in v5.5 and v5.6:

A trigger (…) is not permitted to modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.