Economically it'd be both. Capital flight increases the supply of loanable funds available for foreign investments. Unwillingness to take on foreign investors decreases the demand for this. High supply + low demand = a poor price.
It could be both. We only have evidence for the supply hypothesis (i.e. capital flight). American companies requiring a higher price for foreign investors sounds plausible. But it's a guess for which we have zero evidence, particularly at a systemic level.
(Fixed demand and higher supply still lower prices.)
One test might be found in comparing pricing and flows for foreign investors around investment vectors companies have discretion around (e.g. private investment or M&A) to vectors with which they don't (e.g. public markets). You'd have to control with prices and flows from American investors in those markets, too, which makes it difficult.
