So many variables. Are they older/elderly? Are they disabled? Do they spend much of the week away (at work maybe) and CBA with bothering with the garden? Maybe they are hippies/earth mother types who like the garden to be 'au naturelle.' Maybe they're just not 'garden' people.
If it helps @twiddlingthumbs69 my next door neighbour - woman on her own with 2 young DC, has a garden that is quite overgrown most of the year. In the front garden the lawn gets mowed about 3-4 times a year, it often grows a foot and a half high, and the 'flower beds' are 90% weed. The back garden is 70% patio, and full of weeds in the cracks, and the smallish lawn she has back there is also often a foot and a half high before it's mowed. She also has overgrown bushes, and overgrown trees... Rarely cuts or trims them.
She is a lovely neighbour. Quiet and considerate, and polite. And her 2 DC are polite and pleasant. The only time we hear her and the 2 DC is when they are on the karaoke machine, maybe 3 times a month in the lounge, and it's for about an hour, and not even that loud. (In fact it's quite cute hearing it, because it's quite funny.) When they have visitors, they go to the kitchen/dining area at the side of the house, and we hear nothing then.
So tl;dr I don't think a messy/overgrown garden really means someone is going to be a horrible neighbour. Anymore than a nice, neat garden means someone will be a good/pleasant neighbour.
That garden doesn't even look that bad to me - although it's hard to tell from that one picture...
A bit surprised about a few people saying it could be a magnet for rats though, because as someone said. it's usually food that attracts rats. I did google it, and an overgrown garden can attract rats (moreso than a neatly kept one) but it won't automatically do so.
And, as I said, our next door neighbour has a garden that's overgrown for much of the year, and we have never even seen a rat around here.