The Quick-Start Rules do not constitute Rules-As-Written.
From the official website's products listing:
If you’re new to Shadowrun, dive into the free Quick-Start Rules PDF to get a quick taste of the universe and rules. Once you’ve wetted your appetite, the Fifth Edition Rulebook is the single source you need to dive into all the action, intrigue and magic of all the Sixth World has to offer.
The Quick-Start Rules are designed to introduce new players and transition old players to the latest edition. The Core Rulebook supersedes all previously published material. Whenever the Quick-Start Rules and the Core Rulebook conflict, the RAW position is that the wording in the Core Rulebook is authoritative and takes precedence (unless it is addressed by the Core Rulebook errata, in which case it is authoritative and takes precedence). Therefore, the "if more than half the dice you rolled show a one" wording is correct and is the rule you would be expected to follow if you were engaging in organized SR5 Missions play at a place like GenCon (unless of course the SR5 Missions FAQ says otherwise, which in this case it does not).
Naturally, if you're the GM and you're not in an organized play environment, you're free to decide via house-rule which wording you prefer to follow.
Caveats
This situation leads to some interesting results.
- The general rule in SR5 is to round up unless the text explicitly says otherwise. However if you round up, it penalizes you for having an odd-numbered dice pool by making you more likely to glitch. Therefore I often choose to house-rule rounding down for glitches so that the chance of glitching on a dice pool of 7 is the same as glitching on a dice pool of 6.
- This change actually fixes a longstanding complaint from previous editions where the half or more rule made it almost impossible in practice to not glitch on a dice pool of 2.
- Strictly as a matter of book consistency, the Gremlins quality implies that the rule is still half or more:
For example, a character with a dice pool of 8 and Gremlins level 2 (8 Karma) would trigger a glitch if two or more 1s result from the test (instead of the normal 4).