For Catholics, Saturday evening counts as a Sunday Mass. It's a vigil service, which means it takes place on the evening before (feasts and other importantly occasions often begin at the evening service the night before, probably as a hangover from the Jewish custom of counting days from sunset to sunset rather than sunrise to sunrise). Catholics are supposed to attend Mass every Sunday, and the Vigil Masses on Saturday evenings are supposed to help with this.
The CofE is lax in the sense nobody will try to force you to attend weekly (thought I doubt any Catholic would either), but actually has the same rules - as a Confirmed member you are supposed to attend every Sunday and other days of obligation (as the name suggests!) such as the feasts of Epiphany and Ascension. Most people don't do this but many do.
Those saying he could just attend on another day - Christians have always worshipped primarily on a Sunday because every Sunday is a celebration of the resurrection. Weekday services are a nice to have, but Christians in most denominations are supposed to prioritise churchgoing on Sundays.
And he might be able to attend another service on a Sunday, but bear in mind that if it's important to him to receive Communion then Evensong won't do. Also a brief said early service might not fit the bill if what he wants for his spiritual refreshment is music and the sense of being part of a substantial congregation. Early service in my church is about ten elderly people, while the main service is a hundred and twenty or so of all ages. Perhaps he likes meeting his friends and others at the main service.
And yes it is possible to be a Christian and not to to church, but it's a whole lot harder. Part of being a Christian is being a member of the Body of Christ, the church, and learning and growing together in community. The baptism vows contain solemn promises to be part of the community of faith. Many of us find we need the support of the church, and in turn we need to give the church community our support, because the whole point of Christianity is living in peace and love with one's fellows and the church is how we do that and practice it so we can get better at it more widely in our lives.