If people are following a low carb regime and many have found that a successful way to reduce blood glucose and lose weight then the suggested amount of total carbs not just sugar should be no more than 130g per day. That includes everything you eat and drink. Dividing what you have between your meals rather than a meal with virtually no carbs then a meal with really high carbs would not be quite so good as people can tolerate a certain amount of carbs but more than that will increase their blood glucose too much. Low carb does not mean NO carbs
Can you clarify what the 6.2 is as it could be from a home monitor and would be a moment in time reading in mmol/l or the result of an HbA1C test which would have been in % though now it is more usually given in mmol/mol. The diagnostic level is 6.5% or 48mmol/mol
It is quite possible to manage the condition by diet for many people so he is doing well to lose weight.
This link may help you with some meal ideas.
https://lowcarbfreshwell.co.uk/
The book or app Carbs and Cals is a useful resource as it gives the carb value of various portions of foods and meals so you can meke better choices. It was and still is my bible.
You can also look on packets and on the internet for the Total carbs in the nutritional information, usually given in g carb per 100g so a bit of arithmetic needed to work out for the portion you are going to have.