It is. Google Play reviews are device specific.
As to Bitmart, if you take a look at its reviews from a neutral standpoint--meaning, no devices--what you'll see is 1.3 stars average out of more than 50,000 reviews. It's worth noting that out of the 20 reviews at the top, Bitmart got 18 one-star reviews. Those are phone reviews.
They fare better in Tablet reviews. They got 3.6 on average out of just hundreds of reviews, and 6 non-single star reviews out of the top 20.
Not all reviews are based solely on the type of device. Many users leave reviews based on their experience with the Bitmart platform itself or with its customer support service. If you take a look at Trustpilot, you'll find that the exchange has a TrustScore of 3.1, which it’s not perfect, but quite common among most centralized exchanges.
As for the Bitmart app on the Google Play Store, it's now updated to the latest version, and it's always best to download apps from trusted official stores like Google Play or the App Store. I would also advise the OP not to download it from external links, as there’s a real risk of ending up with a fake app or one that contains a Trojan, or even clicking on a phishing domain imitating the original exchange.