Cogsworth increases Quest Reward XP

I just noticed something odd which I haven't seen mentioned anywhere. I just started Fallout 4 (but burned many many hours on 3 and New Vegas) so I'm wondering if I'm missing something as I'm just learning the mechanics of 4.

I was experimenting with completing a quest with various INT boosts (hat, mentats, x-com, etc.) and I found that having Codsworth as my companion gives an additional XP boost of approximately 5%. At this point I abandoned the original goal of testing mentats, etc. and just focused on the differences of completing the quest with Codsworth, Dogmeat and No Companion (Cods and Dogmeat are my only possible companions at this point in my game). I am only wearing the Drifter Outfit for all of these tests. I am completing the "The First Step" quest and the tests below involve the first award when I say "You know that settlement you sent me to help" and Preston says "…how I ended up as the last one". I'm not sure if it makes a difference but I'd been using Codsworth exclusively for some time, so it's likely that I did most/all of the Quest's 'work' with Codsworth. Also FYI my INT is 6.

I then performed another run introducing whether or not the Well Rested Perk was active (same result):

Finally I finished out the conversation with Preston resulting in him making me the General of the minutemen (honestly I was shocked, it was an honor just to be nominated). Note the numbers below represent the XP awarded in that final step and do not include the XP awarded earlier in our conversation. Same result in this test too

So is this a known perk of using Codsworth? Or does it apply to whichever companion helped me do the quest? Or am I missing something? Or…?

Since Codsworth gets in a twist when you use Mentats, X-Com to boost INT, I assume it's possible the developers gave him a boost to compensate for not using meds with him in tow.

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EDIT: Thanks for the responses! Please forgive my ignorance, this is my first time playing a serious game on a PC (all my years have been on PlayStation and X-Box). So I didn't consider Mods, well b/c this is the first time I've ever used a Mod. I've listed the four I currently have installed below. I can reperform the tests with all of the Mods disabled, however the comment by LordOfWar1775 in which he says "fresh playthrough without mods" makes me think that it would not be a sufficiently 'clean' test. That comment gives me the impression that the only way to be sure would be to start a completely new game with no mods, is that True?

1. Workshop Framework by kinggath
2. Workshop Plus by kinggath
3. Unofficial Fallout 4 Patch by Arthmoor
4. Improved Map With Visible Road by mm137

Unrelated: I'd love to hear your input if you think Mods in general are a bad idea, or if some/all of these four are bad ideas