This was not an ass pull, there is a very logical explanation why Kurama was able to use senjutsu. But before I get to that we must understand a few things.
Tail beast can't use senjutsu. If they could then there would have been no reason for Naruto to need to combine his sage mode with tail beast/chakra mode to counter Obito's TSB.
Kurama can take over Naruto/clone's body. Just like when he took over Naruto's body and gave Kakashi chakra -
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The reason Kurama was able to use senjutsu was because he took over Naruto's clone and used senjutsu through Naruto's clone.