I am a young faculty member and have recently started hiring for my first PhD vacancy. Among my pool of applicants, there was one candidate whose recommendation letter stood out. Allegedly written by a professor at a university in an English-speaking country, who taught a course this student took, this letter included what I would deem excessive praise ("...of all my students, I would rank [student] as the best in terms of creativity, hard work, and breadth." [sic] and "I believe [student] would be one of the most promising students in your university.") and flawed English ("[Student] has very ambitious pretentious [sic] in his field"), which I would not expect from faculty in an English-speaking country. The praise also doesn't align with the grades the student submitted, which indicated that they had to re-take about half of their courses and graduated with a barely passing grade.
Taken together, these factors make me suspicious that the recommendation letter may have been manipulated. However, the recommendation letter was also not written for my vacancy but apparently a prior application to an international M.Sc. programme, and the alleged author and the student both hail from the same non-English-speaking country.
Now my question: Should I inform the alleged author of my doubts regarding the authenticity of the recommendation letter? On the one hand, I myself would like to know if a student ever were to impersonate me in such a manner. On the other hand, voicing my suspicions could be an affront if the recommendation letter is indeed genuine.
Edit / Follow-up: Following the recommendations, I have reached out to the alleged author to confirm the authenticity of the recommendation letter without voicing specific concerns. The professor responded that they "did not approve the letter", which suggests that it was indeed a forgery.