Hickory: The guy rolled for two hours to get this, but why? There's no earthly reason for 18 STR and 18 CON for a mage -- a wiser decision would have been to up WIS to boost identifying things. A solo character is not going to be carrying around enough (inventory limit) to warrant even STR at that level.
pi4t: 18 Con was obviously a mist take: unless all the charts I've seen have been mistaken, non warrior classes gain no benefit for Con above 16. On the other hand, when playing solo you don't have tanks to protect you from being hit. While moving out of the way generally works, there are situations where it isn't feasible, so having extra hitpoints can always be useful. What's more, not having the lore to identify something isn't that major an issue, since you can cast the spell if lore isn't enough (and resting can be done almost anywhere, and with no healer will probably be done a lot, relying on the ring of regeneration). Thus, I feel that in principle maximising Con is preferable to maxing Wis, though in this case points were wasted.
18 Str might have been a bit excessive (considering he didn't need to, eg, carry plate armour for himself, and especially in a game with bags of holding). Again, though, I don't see the point of squeezing every point of lore available - I would have simply let my Str drop a bit, and saved time rolling. The author explains that the biggest reason he boosted Strength, though, was for situations where enemies closed with him and he had to use melee in early BG1, when he didn't have the spellslots for spells in every fight (and, as I'm sure you know, retreat to ranged combat can sometimes be tricky and result in hits which a low-level mage is unlikely to survive). He also needed it to open locked doors pre-knock.
As you highlighted, there is zero benefit of 18 CON for anything but a fighter in BG1, so hit points were not the reason -- 16 is the max needed for any other class.
Having lore is far more important in BG1 than it is in BG2. You simply do not have the spell slots to waste (as a soloist) on Identify, nor the money to spend at temples, and resting continually is just cheesy -- there is no ring of regeneration in BG1 by the way. Maximising CON is absolutely not preferable, because there is absolutely zero benefit, while there is ample benefit for lore bonuses (+10) from WIS.
Regarding the melee closing, a mage has a much better chance of surviving a retreat to ranged (kiting) than going toe to toe (Sleep, Blindness and Horror are a mage's best friend). Regarding opening locks, Knock is only a level 2 spell -- you don't plan your stats based around your character's first four levels if you're planning the long haul.
Way over the top if you ask me.