Venerable Cheng Kuan is the 53rd Generation Acharya of Shingon Shu. Acharya is the rank of the monk. Shingon is the specific denomination. It is Orthodox Esoteric Buddhism. Chan is the chinese name for Zen, another denomination.
If you want to read some good books on Buddhism, my reccomendation is to focus on reading the Buddhism books written by Monks. So there is some legitimacy to the information, otherwise, if you read books by non monks regarding Buddhism, you can just regard that as that persons personal opinion. Make sure not to mistake someones personal opinion as being the offical doctrine of Buddhism. Only monks are allowed to teach the offical positions of Buddhism.
As Huifeng has pointed out so well, ācārya and monk are two different things. Some monks may be that, and some not. Also as Huifeng has clearly pointed out, there are no vinaya-holding monks within the Shingon tradition today. If any Shingon practitioners do hold a genuine vinaya, they received it from another (non-Japanese) tradition, and that should be made clear. As has been pointed out, simply being a monk does not mean one can teach anything. Many laypeople are more learned and skilled at teaching than monks. That's just the way it is.
Enjitsu, if you were really familiar with Shingon Buddhism, you would know that there is no such thing as a "53rd Generation Acharya of Shingon Shu." You would know that a person may be a "50-something generation ācārya (ajari 阿闍梨) of xxx-ryū," which signifies the reception of the denbō kanjō (傳法灌頂) and kechimyaku (血脈) of a certain hōryū (法流), which are the many transmission lineages in which Shingon praxis is transmitted. You would also know that there are literally thousands of people who are ajaris in Japan and some abroad, and that ajari is not in itself a teaching rank or qualification per se in the real world in Shingon, it is the prerequisite for advanced training and for conducting certain ceremonies. It can be earned in about one year through a specific, intensive training program. There are other teaching qualifications beyond it that may be received.
Whether being such an ācārya/ajari qualifies a person to decide on an "Orthodox Buddhism" or "the offical doctrine of Buddhism" that is not "someones personal opinion" I will leave to our readers to consider, if they are so inclined.