Do the 10GB DB size limit in SQL Server Express SKUs also apply to TempDB?

No, it doesn’t. The CheckSize function from the file manager class, which is called when a file is grown or shrinked skips checking for the limits imposed by the SKU when the file correspond to the master, tempdb, or model system databases.

For further information about the “Maximum Relational Database Size” limit imposed by every SKU, refer to the list of Cross-Box Scale Limits section of the Features Supported by the Editions of SQL Server 2014 topic in the documentation of the product.