No, it is not a bug. It is expected behavior and works the same way with tables in Numbers and Keynote.

If you keep creating fresh new tables, they will be named consecutively as "Table 2", "Table 3", etc. However, when you copy and paste an existing table, Pages tries to duplicate it as fully as it can. But because tables are identified by their names, those in the same document need to have different names, compelling Pages to add "-1" while naming the duplicate.