Proving a legal claim is frivolous is a heavy burden. Simply having a losing claim is a long way from satisfying the burden. In British Columbia, a "frivolous lawsuit . . . refers to a legal action that lacks any merit or substance, and is brought forth solely for the purpose of harassing, intimidating, or causing unnecessary expense to the [other party or parties]."
In this case, there is probably enough circumstantial evidence raising a suspicion of undue influence to avoid the will objections being found frivolous.
It is also, however, a heavy burden to show undue influence. Interestingly, while the article cites a number of text messages, none pertain to the will, and the escort claims that she and he never discussed the will. From the very little bit we can see in the article, it would seem that the will contest will be an uphill fight.