The housing situation in the UK is a mess, but blaming this chap for seeing an opportunity to invest money and better himself is no more logical than blaming families for taking up the benefits the government deems them to be entitled to - in each case, if you don't agree with the situation, your beef should be with the elected politicians.
I'm 30, with my own home and one BTL (both in London and surrounds, both bought when I was on a £40,000 salary - it's not a particular achievement). Frankly, having now been in BTL for a few years, I don't have a desire to build a property empire. It is a lot of work sometimes. You are dealing with tenant's homes and you need to act promptly when things go wrong. There is also the (constant) risk of non-payment, not helped by councils refusing the re-house tenants until the bailiffs are on their doorstep. But, when I look at other investment options, I don't see anything nearly as profitable - though I'd much prefer an investment that didn't ring me at 2am because the proverbial boiler had gone.
I do think the subject of that article needs to check what his income from these properties will be like after the tax changes next year - he is "just" a higher earner at £50k, so he may get hammered and find it makes more sense to sell on BTL and pay down the second BTL.