Tulpa, and a number of other similar practices, fall under the category of unfalsifiable. We don't yet have the capability to look into the mind with enough scope to say that this is true or this is false. Moreover, the fact that this whole thing is based on the experience rather than the reality of things, or can be, means that falsifiable is a little bit squishy, one perception of practice could be falsified, but the thing is a whole may remain intact