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Setting an extra liner says they have probably experienced problems with hole stability arising from drilling thru' tricky geology (maybe heavily fractured, cavernous, crumbly, or salt presence). They have earlier mentioned a cavernous section. Setting the liner isolates the problem formation from the hole and allows them to keep drilling. It's usually used as a precaution against the bore hole caving in, in which case they could lose some of the drill string and the bottom hole gear (expensive), as well as delays and cost to sidetrack or re-spud a new well. It's not a decision taken lightly because the new hole must be at a reduced diameter. This place was last drilled so long ago that they might not have detailed records of formations expected t'/be encountered. On balance, it's a good announcement IMO.