Modifying data in a database is a side effect. Since you brought up the wikipedia definition, here it is:
> In computer science, a function or expression is said to have a side effect if it modifies some state outside its scope or has an observable interaction with its calling functions or the outside world besides returning a value. For example, a particular function might modify a global variable or static variable, modify one of its arguments, raise an exception, write data to a display or file, read data, or call other side-effecting functions.
Note "write data to a display or file". I think we agree that writing to a database falls under this definition, hence using terms like "side effecting" when talking about microservices is misleading.