I realize that this was an introductory video to their theory and initial findings, but failing to make any acknowledgement of the fact that correlation doesn't imply causation doesn't seem very rigorous of them. The previous discussion linked to in the OP has a quotation from Geoff Pullum (via roshni) which makes the same point, and then some. I was going type up the same objection to shoehorning languages into "weak FTR" and "strong FTR" boxes myself, but the quotation makes the point better than I could have. I'll repost the quotation here for ease of reference:

If English has future tense markers at all, it has at least a dozen of different ones; but simple use of the present tense is a very prominent way of referring to future time, so what do we make of that? For my part, I have no confidence at all that English is accurately described as "strong FTR". Nearly all traditional grammarians report English as having a tense system that includes a future tense, but that isn't really true; will is a modal auxiliary that has various other uses too. If the facts are shaky for English, how likely are they to be accurate on languages that have not been studied nearly so intensively?

I also worry that it is too easy to find correlations of this kind, and we don't have any idea just how easy until a concerted effort has been made to show that the spurious ones are not supportable. For example, if we took "has (vs. does not have) pharyngeal consonants", or "uses (vs. does not use) close front rounded vowels", would we find correlations there too? I have some colleagues here at the University of Edinburgh, within Simon Kirby's research group, who have run some informal experiments on the data Chen uses to see if dredging up spurious correlations of this kind is easy or hard, and so far they have found it jaw-droppingly easy. (I won't say any more, because I am in the weird position of writing unrefereed telegraphing of unrefereed and informal objections to an unrefereed and unpublished working paper, and it's all getting a bit too weird for me.)

Observing a correlation between the dominant language in a country and the saving habits of that country is well and good, but how, exactly, do they intend to control for cultural differences? How will their theories account for multilingualism or the non-native speakers of a given language in a country, particularly if they form a significant part of the population? How about economic inequality in a given country, what kind of role does that play in saving habits?

I'm not convinced. There are good reasons why strong linguistic relativity has been objected to as vehemently as it has.